Field of the Invention
The present invention relates generally to injection devices for use with an external infusion system wherein a desired therapeutic fluid is subcutaneously delivered to a patient, and more particularly to a disposable subcutaeous injection set having a soft or flexible cannula which is inserted approximately normal to the skin to a desired subcutaneous injection level to deliver the therapeutic fluid with a minimum of discomfort and bother to the patient.
In general, whenever a therapeutic fluid is to be delivered subcutaneously to a patient form an external source, a passageway such as a hollow needle or other type of cannula or catheter device must first be inserted through the skin of the patient in order to provide a passageway or channel through which the fluid may pass from its source external to the patient to the desired subcutaneous location under the skin of the patient. Once this passageway has been installed, any suitable infusion device or system may be used in conjunction with an appropriate catheter connecting the external source of fluid with the passageway leading to the subcutaneous delivery point to deliver the fluid to the patient at an appropriate delivery rate.
Unfortunately, several problems attendant to infusing fluids into the patient as described above are usually encountered. In the first place, it is often uncomfortable, painful, and inconvenient to have a hollow needle or equivalent device piercing the patient's skin for prolonged periods of time. In addition, securing means must be used to keep the needle or equivalent device from moving from or within the injection site as the patient moves about. Such securing means are often quite bulky and bothersome to the patient, as well as being unsightly. There is also a continual risk of infection or inflammation at the skin puncture site. Moreover, the injection system must be primed prior to use. This involves removing all air or other gas from the connecting catheter and needle to thereby allow a known quantity of fluid to be safely dispensed therethrough.
A number of solutions attempting to address these problems have been offered. For example, it is known in the art to insert a soft cannula into the patient rather than a stiff, hard needle or equivalent device. Such a device is shown in U.S. Pat. No. 4,531,937, to Yates. A soft cannula is much more comfortable to the patient than such rigid devices. Insertion is accomplished using a removable stiff needle or stylet that passes tightly through a lumen of the soft cannula. A sharp tip of the needle extends from the end of the cannula when the needle is fully inserted therein. The sharp tip of the needle is inserted into the patient at the desired injection point, with the soft cannula following the needle and thereby being inserted therewith. Once both the needle and soft cannula are thusly inserted, the needle is withdrawn from the cannula, leaving the soft cannula in the patient and providing a more flexible and comfortable passageway through which fluid may be delivered to the patient at the desired subcutaneous site.
In Yates and other similar devices, removal of the needle from the soft cannula leaves an opening through which fluid may leak. While such an opening may be plugged by locating a self-sealing septum in the cannula, the problem of some degree of fluid leakage remains, particularly in those drug infusion systems having fluid delivery pressures much greater than those pressures encountered in gravity-feed injection systems.
Another proposed solution to the foregoing problems is the hard needle injection set, an example of which is shown in U.S. Pat. No. 4,235,234, to Whitney, et al. The injection set includes a locator pad having a sharp rigid needle protruding at a substantially right angle to the bottom surface of the locator pad. The bottom surface of the locator pad typically has a pressure sensitive adhesive applied thereto. Thus the needle is inserted into the skin of the patient while the locator pad is pressed against the skin at the same time in substantially the same motion, thereby securing the needle at the desired location. The needle has a right angle bend therein, positioned in the locator pad, to allow a delivery tube to be connected to the needle in a direction substantially parallel to the skin. This eliminates tubes or needles that might otherwise protrude perpendicularly from the skin, which protrusions can be not only a source of constant irritation and frustration to the patient, but also an easy target for accidental bumping by or entanglement with the patient's external environment.
Despite the beneficial features available with teachings of the art such as Whitney, et al, some problems common to injection sets still persist. For example with hollow needle injection systems a common problem is for the relatively small diameter lumen of the needle to become clogged or otherwise blocked or plugged, thereby preventing the free flow of fluid therethrough. This problem is aggravated in devices having a 90 degree bend placed in the needle, such as, for example, the Whitney, et al device. For this reason most injection sets, unlike the Whitney, et al and equivalent devices, shy away from 90 degree bends in the delivery channel. At most, such other devices utilize a "Y" shape, thereby minimizing the angle or bend in which a blockage could occur.
Another significant problem that occurs whenever a hollow needle or equivalent device (e.g., a solid needle having a channel or groove along one side) is employed to puncture the skin is that of "body coring." Body coring occurs when a piece of body tissue is cored out of the skin as the needle cuts therethrough. This piece of cored-out tissue remains in the lumen or channel of the needle and prevents fluid from flowing therethrough. In many injection systems, such as that illustrated in Whitney, et al, a body core can only be removed by removing the needle from the patient and flushing the system to force the cored tissue from the needle. Unfortunately, upon reinsertion there is a substantial risk that body coring may occur again. In other injection systems, such as those typified by Yates, body coring disadvantageously prevents the system from being primed in the proper manner.
In view of the above, it may be perceived that a substantial need exists for an injection set that combines the advantageous features of the devices discussed above, such as the use of a soft or flexible cannula and the use of a simple low-profile locator pad, but without the disadvantages encountered by such devices, namely the difficulties associated with priming and sealing the devices, and the problems associated with blocking or plugging of the devices.